Why Does Tripper Arm Gear Keep Breaking

Repeated failure of the Tripper Arm Gear ( and /or the # 7 gear that drives it ), is caused by the timer assembly "binding" internally.
The gears get "sloppy" over time, and the # 8 drive gear will start rubbing against the Output Gear center hub. This added pressure makes the already difficulty job of the Tripper Arm Gear impossible.
It's pushing the Skipper Wheel, which in turn is pushing on the "tab" of the Output Gear, and the Camshaft must also be turned a little, before the Output Gear "catches" the Drive Gear # 8, and the motor turns moving everything.
It's very common problem as the 440 timer "ages", and best solved by complete replacement of the Timer Assembly with the newer 460TC ( the current replacement for all 440 series timers ).

Also the "Out Put Connector" # 21E ( 1031496 ) which which attaches to and drives the Cam Shaft can crack or break. On rare occasions the Camshaft # 21F-3 ( 1031950 ) will break at one end. Also, rare is a cracked Skipper Wheel # 14F-6 ( 1031740 ). Close examination of both sides of the Skipper Wheel is required to detect this failure. And last, but not least, you can have a gear post break in the housing body it's self. But only the back plates for the 440i version is available and not the "box" used with the older 440 version. It is simpler and prudent to replace the Complete Timer Assembly ( with the new 440iHV ) at this point.